In recent years, the combination consisting of a positron emission tomograph and a conventional computed tomograph (for instance, x-ray tomograph) has become an accepted and widely applied imaging solution in the field of medical imaging diagnostics. The functional PET images and the higher-resolution CT images together provide valuable diagnostic information. Images provided by the PET arrangement may be advantageously combined also with MRI images.
In early solutions the separate PET and CT apparatuses adapted for examining human subjects were first combined, and were later accommodated in a common housing. Such apparatuses are disclosed for instance in US 2011/0224534 A1, US 2011/0077511 A1, US 2012/0046544 A1, US 2012/0085912 A1, and US 2012/0271164 A1. In the case of these apparatuses, the diameter of the bore or examination space adapted for receiving the patient is typically 600-800 mm, which makes these apparatuses suitable for performing whole-body scans. These scanners are thus suitable also for brain scans, but their resolution is limited due to the large diameter of the examination space.
For the above reasons, different types of apparatuses have been developed for examining small animals. In these apparatuses PET scanner rings of smaller diameter are applied, and the imaging field of the applied CT scanners is also much smaller. Such apparatuses are primarily suited for examining mice and rats, and have a bore size far smaller (60-110 mm) than the above introduced apparatuses. Accordingly, their resolution is on an order of magnitude better than the resolution of apparatuses adapted for performing human whole-body scans. Such an apparatus is disclosed for instance in the document with publication number WO 2012/171029 A1. In the apparatus according to the document, a specimen stage is rotated relative to the PET and CT scanners.
Other than combined PET/CT whole-body scanners, there are only a few prior art devices capable of examining the brain, skull or limbs of human or primate animals by combined PET and CT scanning. Such a solution is for instance the so-called NeuroPET-CT device, wherein the PET scanner ring is disposed behind the CT scanner. Because of the fairly large longitudinal size of the CT arrangement, the PET scanner ring has a considerably large blind area.
A portable PET detector capable of performing PET brain scans is presented in WO 2010/033159 A1. In addition to apparatus with such helmet-like detectors, a mobile apparatus comprising a foldable detector is also known, as described in US 2012/068076 A1. A similar apparatus is disclosed in U.S. Pat. No. 5,420,427. An apparatus capable of performing brain scans applying a PET scanner ring mounted on a movable gantry is described in US 2011/127434 A1.
Similarly aimed solutions for performing only CT scans are also known, e.g. from WO 2011/135185 A1, WO 2011/135186 A1, WO 2011/135187A1, and WO 2011/135191 A1. A similar concept is spelled out in US 2006/067464 A1.
Further PET-CT scanners, capable basically of performing whole-body scans, are described in US 2012/0265050 A1, U.S. Pat. No. 6,670,614 B1 and U.S. Pat. No. 8,351,566 B2. These apparatuses have the common disadvantage that the components adapted for taking the PET and CT images are arranged along the same circumferential region of the examination space such that they have overlapping fields of vision, which means that the PET components are arranged along a first portion of the circumference of a given slice of the examination space, the CT components being arranged along a second portion thereof. Therefore, there are configuration limitations for the PET and CT units in case of these solutions: for instance in certain solutions the PET detector cannot be ring-shaped because the PET detector units can only be arranged in a given region of the circumference.
In WO 2012/066469 A1 a detector is described that is capable of detecting particles generated during both PET and CT scans. In US 2012/0161014 A1 an arrangement is disclosed wherein the PET scanner arrangement comprises a plurality of PET rings, with CT apparatuses being disposed between neighbouring PET rings. A combined PET-CT apparatus is disclosed in DE 10 2007 061 596 A1.
U.S. Pat. No. 8,232,527 B2 discloses a PET apparatus comprising a secondary radiation source disposed in the examination space, the PET scanner ring being thus capable of detecting the radiation of the secondary radiation source in addition to radiation coming from the examination subject.
A combined PET-CT scanner apparatus adapted for taking whole-body scans is described in U.S. Pat. No. 7,652,256 B2. The scanner comprises a conventional CT apparatus, with a PET scanner insert extending to a small extent into the examination space of the CT scanner being incorporated in the apparatus. In U.S. Pat. No. 7,053,376 B2 a combined PET-CT scanner apparatus adapted for performing whole-body scans is described wherein a CT radiation source extends into the PET scanner ring. In U.S. Pat. No. 7,053,376 B2 such embodiments are also described wherein the PET scanner ring is arranged in a way similar to what is disclosed in US 2012/0161014 A1.
The prior art also comprises combined PET-MRI apparatuses.
In light of known solutions the need has arisen for a combined tomographic apparatus that comprises a PET arrangement and a second imaging arrangement—preferably a CT arrangement or MRI arrangement—, and is particularly adapted for examining the brain or a limb of a human and/or primate animal, and therefore the PET ring can preferably be dimensioned accordingly, and which apparatus allows performing a PET scan and a second imaging examination in a more advantageous manner than the known solutions, in such a way that the examination subject either does not need to move during the examinations, or needs to move only to a small extent and in a controlled way.